From b55397ea5ddb09dbeab355cbb81fa07f6fbd413f Mon Sep 17 00:00:00 2001
From: "Jan (janneke) Nieuwenhuizen" <janneke@gnu.org>
Date: Fri, 27 Mar 2020 21:29:23 +0100
Subject: [PATCH] Make `read-bytes' suspendable for socket reads on MinGW.

On MinGW, port-read will block on sockets if no data is available.
Avoid blocking by using select first.

* module/ice-9/suspendable-ports.scm (read-bytes): For socket ports,
guard port-read with select.
---
 module/ice-9/suspendable-ports.scm | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/module/ice-9/suspendable-ports.scm b/module/ice-9/suspendable-ports.scm
index 9fac1df62..720f10c0f 100644
--- a/module/ice-9/suspendable-ports.scm
+++ b/module/ice-9/suspendable-ports.scm
@@ -68,8 +68,12 @@
 (define (wait-for-writable port) ((current-write-waiter) port))
 
 (define (read-bytes port dst start count)
+  (define (socket? port)
+    (string-prefix? "#<input-output: socket" (format #f "~a" port)))
   (cond
-   (((port-read port) port dst start count)
+   ((and (or (not (socket? port))
+             (pair? (car (select (list port) '() '() 0 0))))
+         ((port-read port) port dst start count))
     => (lambda (read)
          (unless (<= 0 read count)
            (error "bad return from port read function" read))